In the treatment of slurries of comminuted cellulosic fibrous material (i.e. paper pulp slurries), the common practice when bleaching with chlorine is to introduce chloride gas mixed with water into a low consistency slurry, that is a slurry having a solids concentration of between about 1-5 percent. The chlorine gas and water are usually introduced into the slurry at a conventional mixer inlet. The gas and slurry are mixed together by the mixer, and when discharged from the mixer may additionally be passed to another mixer for further mixing action.
According to the present invention it is desirable to introduce chlorine gas into a paper pulp slurry to effect treatment thereof in manner that is simplified compared to the prior art, and which allows for more versatile mixing of the chlorine gas and the pulp, and additionally allows the introduction of a higher volume of gas into the pulp with effective mixing.
According to one aspect of the present invention, the volume of gas that may be introduced into the slurry is enhanced by providing the gas in a flow controlled pathway, splitting the pathway into at least two (i.e. a plurality of) paths, and directing each path to an inlet to a mixer, the mixers connected in series in the flow of low consistency pulp stock.
According to another aspect of the present invention, it is possible to enhance the flexibility of the chlorine gas bleaching of pulp by mixing the gas into a medium consistency paper pulp slurry (e.g. a slurry having a consistency of between about 6-15 percent, and preferably between about 8-12 percent). The chlorine gas may be introduced directly into the inlet to a fluidizing mixer, and there is no necessity or desirability of introducing the gas with water. The fluidizing mixer, which may be of the type such as shown in U.S. Pat. Nos. 4,577,974 or 4,543,181, or that sold commercially by Kamyr, Inc. of Glens Falls, N.Y. and Kamyr AB of Karlstad, Sweden under the trademark "MC", effects fluidization of the pulp, intimately mixing the gas and pulp together. In order to increase the volume of chlorine gas added, and obtain enhanced mixing, it is desirable--as in the case of the low consistency pulp--to split the flow controlled pathway of chlorine gas into a plurality of paths, each path leading to the inlet to one of a series of connected fluidizing mixers. Preferably two mixers are utilized.
It is the primary object of the present invention to provide for the enhanced effectiveness of the introduction of chlorine gas into a paper pulp slurry for treating the slurry with the chlorine gas. This and other objects will become clear from an inspection of the detailed description of the invention and from the appended claims.